DTC P1621 Control Module Long Term Memory Performance. Chevrolet PJJ 2000

For 1990-2009 cars

### Circuit Description

The Powertrain Control Module (PCM) is the control center of the fuel injection system. It constantly looks at the information from various sensors, and controls the systems that affect vehicle performance. The PCM also performs the diagnostic function of the system. It can recognize operational problems, alert the driver through the malfunction indicator lamp (MIL) (Check Engine), and store a DTC or DTCs which identify the problem areas to aid the technician in making repairs.

### Conditions for Setting the DTC

The PCM cannot communicate internally.

### Action Taken When the DTC Sets

• | The malfunction indicator lamp (MIL) will illuminate.

• | The PCM will attempt to record the operating conditions at the time during which you detect this failure, however, since this is a internal PCM failure, you cannot rely on this information. This information will store in the Freeze Frame and Failure Records buffers.

• | A history DTC stores.

### Conditions for Clearing the MIL/DTC

• | The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.

• | A history DTC will clear after 40 consecutive warm-up cycles without a fault.

• | Use a scan tool to clear the DTCs.

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.

2. Reprogram the replacement PCM and perform the crankshaft position system variation learning procedure. Refer to the latest Techline information for PCM programming and CKP System Variation Learn Procedure .

#### DTC P1621 PCM Memory Performance

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check

2

1. Turn OFF the ignition switch.

Important: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .

2. Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the repair?

--

Go to Step 3

--

3

1. Using the scan tool, clear the DTCs.
2. Start the engine.
3. Idle the engine at the normal operating temperature.
4. Operate the vehicle within the conditions for running this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic has ran and passed?

--

Go to Step 4

Go to Step 2

4 | Check to see if any additional DTCs are set. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK